Prestressed unit



Feb. 2, 1965 G. J. YEVICK 3,168,020

PRESTRESSED UNIT Filed Nov. 25, 1960 INVENTOR GEORGE J. YEVICK United States Patent 3,168,020 PRESTRESED UNIT George .I. Yevick, New York, N.Y. (536 Nordlioff Drive, Leonia, NJ.) Filed Nov. 25, 1960, Ser. No. 71,534 7 (Ilairns. (Cl. 94-8) It is known in the structural arts that economies may be effected by the utilization of certain materials such as concrete which have been prestressed. In their normal state, such materials often exhibit a greater resistance to compressive stresses than to tensile stresses. By various schemes structural units fashioned from such materials may be placed in a desired state of compression so that during their subjugation to external structural loads the resultant stresses within the material may be withstood without failure of the material.

Prior methods of introducing desired stress into a structural unit formed of such a material have often utilized a tensioned, elongated rod of steel or other substance having a high tensile strength which passes through the unit. The resultant compressive force due to the tensioned member acts against two opposed points or sides of the unit where the ends of the tensioned member, often provided with hearing plates, contact it.

By the present invention, however, compressive force acts over a continuous circumferential zone of the material thus giving rise to oppositely directed compressive stresses over an infinite number of opposite points or sides. Further, the invention utilizes this novel compressive stress distribution in combination with a reticulate configuration of the steel or other substance having a high tensile strength within the structural unit. Thus the advantages of the above novel stress distribution are combined with the excellent strength-to-weight ratio of a reticulate structural configuration.

According to the invention, a prestressed structural unit is formed of a reticulate member whose cells or interstices contain blocks which are compressed over a continuous circumferential zone or portion of their area. The unit is formed by inserting the blocks in the cells of the reticulate member and then circumferentially contracting them about the blocks. The structural unit may be used as a modular unit of construction.

One example of the utility of the invention is afforded by its use as a roadbed. In this example the reticulate member is fashioned from steel and the blocks are of concrete. As is well known, many concrete roadbeds fail due to tensile stress in the concrete caused by low temperatures and/ or load changes. By prestressing each concrete block in accordance with this invention it may be caused to remain under compressive stress during wide temperature and load variations thus precluding failures due to tensile stresses within the concrete.

A difficulty encountered in the fabrication of such units is effecting the cross-sectional shrinkage of the cells in the reticulate grid element. This is particularly so in making a roadbed in situ. According to this invention, the cross-sectional area of the cells of the reticulate grid is caused to diminish by the use of shims or wedges driven between double walls of the grid element.

In the drawings:

FIGURE 1 is a perspective view of a segment of a reticulate grid of the invention;

FIGURE 2 is a cross-section taken along line 2-2 of FIGURE 1;

FIGURE 3 is a view similar to FIGURE 1, showing the concrete block elements within the cells of the grid and also showing the shim or wedge elements in place;

FIGURE 4 is a view taken along line 44 of FIGURE 2; and

FIGURE 5 is a perspective view of one form of a wedge or shim element employed to effect diminution of the cells of the grid element.

Referring now to the drawings, FIGURE 1 shows a segment of a reticulate grid 10 having hexagonal cells or interstices 12. There are two walls 14 bounding each cell 12, these Walls being joined along their lower edges thereof by bight portion 16. The exact manner of fabrication of a reticulate grid element having this double wall construction forms no part of the present invention.

As shown in FIGURE 3 of the drawings, concrete block elements 18, formed in any desired manner, of substantially the same cross-section as cells 12 are now placed within each cell. Shims or wedges 20 are now driven between the walls 14. The width or thickness of the shim elements 20 is slightly greater than the distance shown in FIGURES l and 2 between each wall 14. Preferably, the lower edge of each shim is rounded as at 22 to facilitate easy driving of the wedges downward. With the wedges in place, the cross-section of each cell 12 is now slightly diminished, thus exerting compressive stresses around the circumference of each block 18. FIGURES 3 and 5 show the wedges or shims 20 as each comprising three legs or radiating sections. However, those at the periphery of the grid 10 have only two legs, as shown at the lower portion of FIGURE 3 of the drawings. Within the scope of the invention however the shape of the shims may be varied.

It will be observed that the fabrication of such a prestressed structural unit is quite simple. Any device may be used to drive the shims down between the walls 14 to cause compression of the blocks 18. In the event that asymmetrical compressive stresses are desired in any of the blocks 18, the shims adjacent such blocks would be correspondingly varied in thickness from top to bottom to give such stresses.

I claim:

1. A prestressed structural unit comprising a reticulate member whose cells are each bounded by two spaced walls, blocks of the same cross-sectional configuration as that of the said cells in the said cells, shim elements extending between the spaces between the said spaced walls and urging the spaced walls apart, the said blocks being in compression over a continuous circumferential zone.

2. The prestressed structural unit of claim 1 wherein the said blocks are formed of concrete.

3. The prestressed unit of claim 1 wherein the height of said walls and the thickness of said blocks are equal, whereby each portion of each of said blocks is under radial compression.

4. The prestressed structural unit of claim 1 wherein said shim elements have parallel sides which engage the said spaced walls.

5. The prestressed structural unit of claim 1 wherein the said spaced walls are joined at corresponding edges.

6. The method of making a prestressed structural unit comprising the steps of placing into the cells of a reticulate member, each of whose cell walls are bounded by double walls, blocks of the same cross-sectional configuration as that of the said cells, and then permanently increasing the spacing between the double cell walls to thereby stress the blocks over a continuous zone.

7. The method of claim 6 wherein the spacing between the cell walls is increased by driving wedge elements therebetween.

(References on following page) "I 0 References Cited by the Examiner UNITED STATES PATENTS 96,918 11/69 Howard 94-14 1,645,622 10/27 Prince 948 1,885,720 11/32 Hewett 94-11 4 1,982,110 11/34 Keown 948 2,251,672 8/41 Friberg 94-18 X 2,921,462 1/60 Wilson 50441 5 JACOB L. NACKENOFF, Primary Examiner.

WILLIAM I. MUSHAKE, Examiner. 

1. A PRESTRESSED STRUCTURAL UNIT COMPRISING A RETICULATE MEMBER WHOSE CELLS ARE EACH BOUNDED BY TWO SPACED WALLS, BLOCKS OF THE SAME CROSS-SECTIONAL CONFIGURATION AS THAT OF THE SAID CELLS IN THE SAID CELLS, SHIM ELEMENTS EX- 